This invention relates to a method for preparing a resin-reinforced decorative board. More specifically, it relates to a method for preparing a resin-reinforced decorative board in which a resin-reinforced decorative veneer and a base board are integrally adhered.
A resin-reinforced decorative board obtained by the simple and easy method of the present invention exhibits the beautiful woody appearance inherently possessed by a decorative veneer and also has excellent durability. The resin-reinforced decorative board of the present invention is suitable for use as a decorative plywood having natural woody appearance or a flooring plywood.
Heretofore, natural wood decorative plywood on which decorative veneers, sometimes called fancy veneers, had been adhered to the surfaces of the plywood have been commercially available. In order to improve the dimensional stability or the mechanical strength of the decorative veneer, a resin forming component had been permeated into the decorative veneer and polymerized.
In general, reinforcement of the decorative veneer was carried out by impregnating the veneer with a resin forming component, such as a resin liquid, followed by polymerizing. One such technique, called WPC (Wood Plastic Combination), is one where the wood and the resin are formed into a composite using a monomer or an oligomer as the resin liquid.
Preparation of a decorative board according to the WPC technique is generally carried out by placing the decorative veneers in an autoclave and then reducing pressure therein in order to remove air from decorative veneers. This is followed by injecting a resin forming component such as a monomer, an oligomer, etc., under pressure into the autoclave to permeate the veneers. The veneers are then taken out of the autoclave and separated. Plywood, which is to serve as a base board, is coated on at least one surface with adhesive. The resin permeated decorative veneer sheet is then placed on the adhesive coated surface of the plywood to form a composite. This composite is then heated and pressurized by a hot press thereby effecting polymerization or polycondensation of the resin-forming component as well as adhesion of the decorative veneer sheet and the plywood (Japanese Laid-Open Patent Application No. 75713-1973). However, this method involves a problem in that it requires many steps such as the reducing and pressurizing steps in the autoclave, the separation of the veneer sheets, the adhesive coating of the plywood, the placing of the veneer sheet permeated by the resin-forming component on the surface of the plywood, and the hot pressing, etc. Further, this method involves problems not only requiring multiple steps, but also other complicated problems. For example, the veneer sheets, into which a resin-forming component is permeated, are adhered to each other by the resin-forming component because they are thin. Thus, it is difficult to separate these sheets from one another. Also, when separating the sheets, the veneers sheets sometimes crack or defects occur so that many losses result due to damage to the sheets. This results in lowering the production yield of the products.
There is also a method in which decorative veneers are placed in an autoclave, air in the veneer sheets is removed under reduced pressure, a resin-forming component such as a monomer, an oligomer, etc. is injected into the autoclave, the atmosphere is pressurized in order to permeate the resin-forming component into the decorative veneers, the sheets are then taken out of the autoclave and peeled to separate respective sheets, and a polymerization reaction is effected in a hot press, etc. Thereafter, in the same manner as in the preparation method of usual decorative boards, an adhesive is coated on a base board and the WPC treated decorative veneer is placed on the base board and adherence is caused by hot pressing. However, in this method, there are problems because the steps are complicated. Furthermore, the resin-reinforced decorative veneer formed by the WPC technique is prone to warpage or cracking which leads to lowering the yield and therefore results in poor productivity. Further, in either of the above methods, a resin-forming component is permeated into the inside of decorative veneers from substantially all surfaces of the veneer sheets. Therefore, control of the degree of permeation is difficult. Thus, controlling the wood grain appearance of the decorative veneer is difficult. The beautiful appearance possessed inherently by a wood decorative veneer tends to be lost.
Further, when adhesion takes place, heating and pressurizing are often carried out and the viscosity of the adhesive tends to decrease abruptly due to the heating. In this case, the adhesive tends to flow out from its location between the decorative veneer and a base board or a strong run-off can be ejected from an opening or cracked portion of the veneer sheet. Therefore, it is necessary to control the viscosity of the adhesive, and the heat and pressure conditions. These operations are complicated, and a thick adhesive layer can be difficult to form.
Furthermore, a resin-reinforced decorative board obtained by this method has poor durability when subjected to repeated cool-hot cycles which easily cause cracking in such decorative veneers. It is the present state of the art that even when a coating is applied to the surface of a decorative board, durability is still poor.